Rechargeable bipolar high power electrochemical device with reduced monitoring requirement

ABSTRACT

The present invention is drawn to a high power electrochemical energy storage device in a bipolar configuration, comprising at least n stackable cells in bipolar configuration wherein subgroups of m cells are electronically monitored. The storage cells have a lithium ion insertion anode and a lithium ion insertion cathode, a separator, an electrolyte system, and a leak-proof seal structure. A number of embodiments are disclosed, characterized by a favorable range of m values, in combination with the anode-to-cathode capacity ratio, electrolyte conductivity, and other battery key features, thereby providing a high power device providing long cycle life and excellent power performance over many thousand charge and discharge cycles while minimizing the cost for electronic monitoring. Additionally, the present invention is drawn to a device combining two or more groups of stackable cells in bipolar configuration, either in series or in parallel or any combination thereof, so as to create a high power, high voltage energy storage device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national phase application under 35 U.S.C. §371 ofInternational Application Number PCT/EP2004/009183, filed on Aug. 16,2004, which claims priority to U.S. Ser. No. 60/495,324, filed on Aug.15, 2003, both of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates in general to electrochemical devices,and, more particularly to a high power electrochemical device in bipolarconfiguration capable of providing instantaneously available high power.The high power device is based on a nonaqueous electrolyte systemcontaining lithium salt. Anode and cathode are constructed from highrate, highly stable and low cost materials and are selected to providemaximum device safety. Additionally, the present invention relates tothe number of voltage-monitored cells connected in series in a bipolarconfiguration, in combination with the anode-to-cathode capacity ratioand with other device parameters, in order to provide an overalllow-cost system having excellent cycle life and outstanding powerperformance.

2. Prior Art

The need for power quality is ever increasing. Current and futuresophisticated electric and electronic devices are, and will continue tobe, increasingly sensitive to power supply issues. For example, poorpower supply and transient power losses in supplied main power can havean adverse impact on electronic equipment. Such power issues can resultin the destruction of electronic equipment, the loss of generated data,the loss of communication with other equipment, and the loss of timerequired to reset and restart procedures that were interrupted by thepower failure. Certain solutions have been developed to provideinstantaneous power in response to transient power interruptions andother associated power problems, including uninterruptible power supply(UPS) systems. In such systems, lead-acid batteries are often used toprovide temporary power when necessary. While such solutions have hadsome success, lead-acid batteries have certain problems, including, butnot limited to, unsatisfactory cycle life, a high failure rate, highcost of maintenance, high weight, large size, toxicity of the batterymaterials, risk of hydrogen leaks posing a safety hazard, self dischargeissues, and sensitivity to deep discharge and to temperature.

Another important area of application for high power electrochemicaldevices is in the automotive industry for hybrid electric vehicles andfor a wide range of power assist functions. In order to reduce airpollution, particularly in congested cities, fuel efficiency needs to befurther increased. This objective can be achieved by battery systemscapable of providing instantaneous power for acceleration and hillclimbing and the capability for regenerative braking. Such batterysystems have to be able to provide and/or to absorb significant amountsof power over the relatively short period of a few seconds only. Inaddition, there is an increasing array of electrically powered ancillarysystems in modern cars, e.g. for preheating catalytic converters, forelectric brake or steering force amplifiers, drive. by wire,electrically controlled shock absorbers, and the like.

These and other applications for industries including, but not limitedto, car manufacturers, providers of public transport, power quality,power back-up systems, and remote area power supplies in combinationwith wind turbines, photovoltaic cells and/or an electricity generatorbased on fossil fuels such as diesel or natural gas, will increasinglyrequire compact and low-cost storage systems capable of delivering largeamounts of electrical power from a limited volume. In order to fulfillrequirements for such power systems, the present invention is directedto an electrochemical energy storage device, such as a rechargeablebattery device, wherein both the cathode and the anode are constructedfrom high rate, highly stable and low cost materials and assembled in abipolar configuration. While battery devices exist in the older batterytechnologies of lead-acid, nickel-cadmium, and nickel-metal hydride,large high power Li-ion batteries have not been introduced insignificant quantities to the market place yet, mainly due to safetyconsiderations and due to the requirement of single cell control.Electronic control of each cell would add considerably to the cost andthe complexity of high voltage, high power back-up or power assistsystems based on standard Li-ion batteries. It is therefore an object ofthis invention to provide a means whereby electronic control can bedrastically reduced.

A Li-ion battery comprising lithiated titanate anodes, manganeseoxide-based cathodes, and a poly(acrylonitrile) polymer electrolyte hasbeen described, for example in U.S. Pat. No. 5,766,796. Such aconfiguration is however not in the spirit of the present inventionsince the capacity utilization at rates being significantly larger than10C is too low for high power applications. Battery discharge and chargecurrents are often given in “C”-rate. 10C corresponds to ten times theamount of current in relation to the amount of battery capacity (e.g. a10 Ampere current for a 1 Ampere hour battery). A bipolar Li-ion batterydevice with excellent high power performance, stability, and safetycharacteristics has recently been disclosed in PCT Application“rechargeable High Power Electrochemical Device.” Those skilled in theart will appreciate that a bipolar configuration with a maximum numberof cells in series leads to a battery with maximum energy density and alower cost for electronic monitoring of the battery. On the other hand,too many cells in series without electronic monitoring may limit batterylife because slight differences from cell to cell may lead to voltagedifferences during charge and discharge. If one or several cells arecontinuously slightly overcharged battery life may be reduced. Nooptimum number of cells connected in series without electronicmonitoring can be given from first principles. We discovered that thereis a complex and unexpected interrelationship between battery life andbattery design parameters including, but not limited to, the number, m,of cells in a voltage-monitored subgroup in a bipolar battery,anode-to-cathode capacity ratio, and electrolyte properties such asconductivity. It is, therefore, an object of this invention to providekey features enabling a high power battery in bipolar configuration tohave long cycle life and excellent power performance over tens ofthousands of discharge and charge pulses while minimizing the cost forelectronic monitoring.

These and other objectives will become apparent in light of thespecification and claims appended thereto.

SUMMARY OF THE INVENTION

The present invention is directed, generally, to a high power batterycomprising at least one stackable battery unit capable of producing highpower upon demand. The battery unit includes at least two sealedelectrochemical energy storage cells connected in series, preferably inbipolar configuration. The cells have a lithium ion insertion anode anda lithium ion insertion cathode and a bipolar current collector betweencells. The device also has the at least two storage cells substantiallyaligned adjacent one another, a separator material associated betweenthe anode and the cathode within each cell, an electrolyte system withineach cell, and a seal structure providing a liquid-proof seal.

Preferably, the anode of the present invention comprises a lithium ioninsertion material having a voltage of greater than 0.5 V vs. the Li/Li⁺potential, and even more preferably, a voltage of approximately 1.5 Vvs. the Li/Li⁺ potential. For example, the anode could include alithiated titanium oxide. The cathode preferably includes a dopedlithium manganese oxide or any other low cost material offering highstability, high safety and sufficient rate performance such as LiFePO₄or layered manganese-based oxides, modified by elements such as nickeland/or cobalt. Once assembled, it is preferred that the device has acharge and discharge capability of at least 0.04 A/cm² for more than 30s and preferably for more than 60 s.

In one preferred embodiment of the present invention, the devicecomprises two end plates at either end of the aligned at least twostorage cells, each end plate comprising an electrically conductivesurface area, and two terminal plates conductively associated with theend plates, wherein the terminal plates of the device are electricallycontacted over at least 20% of the end plate surface area by at leasttwo contacting means. The contacting means includes, but are not limitedto, an electrically conductive film, a mat of electrically conductivefoam, felt, and expanded or a woven metal mesh The contacting means maycomprise mechanical pressure or the electrical contact may be achievedthrough any welding, soldering, bolting, or crimping process, or throughthe use of electrically conductive adhesives. In the aforementioned caseof mechanical pressure, the mechanical pressure may be applied by amechanical device including, but not limited to, nuts and bolts, springloads, shrink tubing, elastic or inelastic straps, or a housingcontaining vacuum of up to minus one atmosphere relative to ambientpressure. It is also preferred that one or more terminal cables arejoined to each of the two terminal plates to provide the electricalconnection to the entire battery device.

In the invention, it is preferred that the electrolyte system comprise anonaqueous electrolyte system. A number of electrolyte types can beeffective in this environment, including a lithium-based salt selectedfrom the group consisting of LiPF₆, LiBF₄, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂,LiC(SO₂CF₃)₃, LiClO₄, LiF₆, lithium bisoxalatoborate and other lithiumborates. Preferably, the present embodiment also includes at least oneelectrolyte solvent, wherein the at least one solvent is associated withthe electrolyte. Preferably, the at least one electrolyte solvent has aboiling point of 80° C. or greater, most preferably 150° C. or greater,in order to allow for safe device operation up to at least 60° C., evenunder severe conditions. It is also preferred that the solvent isselected from the group including, but not limited to,propylenecarbonate, ethylenecarbonate, diethylcarbonate,dimethylcarbonate, ethyl-methylcarbonate, gamma-butyrolactone,ethylacetate, ethylbutyrate, ethylpropionate, methylbutyrate,1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methoxyethylether,methoxypropionitrile, valeronitrile, dimethylacetamide,diethylacetamide, sulfolane, dimethysulfite, diethysulfite,trimethylphosphate and ionic liquids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic of a three-cell bipolar battery(n=3) in accordance with principles of this invention;

FIG. 2 is a cross-sectional schematic of a twenty-cell bipolar battery(n=20), comprising means for 5-cell monitoring (m=5) as a monolithicunit in accordance with principles of this invention;

FIG. 3 is a graph displaying the capacity output as a function of cyclenumber for EXAMPLES 1-4 of the present invention;

FIG. 4 is a graph displaying the high power discharge profiles forEXAMPLES 1-4 of the present invention;

FIG. 5 is a graph displaying the high power discharge profiles forEXAMPLES 5 and 6, in comparison with EXAMPLE 1 of the present invention;

FIG. 6 is a graph displaying the high power discharge profiles forEXAMPLES 7 and 8, in comparison with EXAMPLE 5 of the present invention;

FIG. 7 is a graph displaying the capacity output as a function of cyclenumber for EXAMPLE 9 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there will herein be described in detail and shown in thedrawings, several specific embodiments with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the inventionto the embodiments so illustrated.

The present high power battery device has at least one bipolar plate 22,and at least two endplates 32′, 32″. FIG. 1 exemplifies an embodimentconsisting of two bipolar plates 22 and two end plates 32′, 32″ stackedon top of each other, resulting in three electrochemical energy storagecells connected in series in a bipolar configuration. Each of theelectrochemical energy storage cells 20 contains two substrate plates21, 21′, an electrochemically active anode layer 24, anelectrochemically active cathode layer 26, a separator 34 and anadequate amount of electrolyte solution 36. FIG. 1 shows as a specificembodiment an example where at least one substrate plate 21′ is commonto two adjacent cells. The substrate plates are preferably of highelectrical conductivity and relatively thin, i.e. preferably betweenapproximately 10 and 100 micrometers, more preferably between 15 and 50micrometers. Aluminum, nickel or copper-aluminum or copper-nickelbimetallic current collectors may be considered. The substrate plates21, 21′ can optionally be covered on at least part of at least one sideof the substrate plates by a layer of primer 40. The primer 40 is basedpreferably on a carbonaceous film. It may be deposited from awater-based ink containing carbonaceous particles and a suitable binder,such as is available commercially from ACHESON®, or as disclosed in U.S.Pat. No. 6,087,045. However, any other conductive material, or any othertechnique such as spray, plasma, sputter, or vacuum deposition can beused, as long as it is deposited on a secure, conductive surface is ontowhich anode film 24 and cathode film 26 may be applied.

Anode 24 and cathode 26 comprise lithium ion insertion materials. In apreferred embodiment, these lithium ion insertion materials are combinedwith a binding agent to create a paste containing the active material ofthe cell and possibly a conductivity-enhancing agent such as particulatecarbon or nickel. This paste is then applied to at least one side ofsubstrate plates 21, 21′ creating a film. It should be noted that bothanode 24 and cathode 26 can be used in a variety of forms, but for thesake of simplicity will be referred to as “films” throughout thefollowing discussion. Films are dried and compacted after application inorder to obtain the desired electrode porosity, preferably in the rangeof 30-60%. Electrode compaction can be achieved through a calenderingprocess, through two or several rolls, or through any other processapplying sufficient mechanical pressure, or a combination of mechanicalpressure and heat. Alternatively, the electrodes can be applied in anypattern. Patterning may be advantageous for processing reasons.

Preferably, lithium ion insertion materials comprise any of a number ofmaterials capable of providing at the same time high-power, high safetyand relatively low cost of the electrochemical storage device. Forexample, cathode 26 of the present invention preferably comprises adoped lithium manganese oxide cathode, most preferably of the spineltype. Alternatively, the cathode could comprise LiFePO₄ or layeredmanganese-or nickel-based oxides, modified by elements such as Al, B,Ca, Co, Cr, Fe, Mg, Mb, Ni, Zn. Similarly, anode 24 preferably comprisesa lithiated titanium oxide anode, such as LiTi₂O₄, Li_(4+x)Ti₅O₁₂, orLi_(x)TiO₂. In the most preferred embodiment, the anode material is ofthe spinel type.

The anode materials disclosed above provide an important characteristicto the present invention. The use of, for example, a lithiated titaniumoxide anode ensures a relatively positive electrode potential of around1.5 V vs. the Li/Li⁺ potential. This potential provides, in contrast tostandard lithium-ion cells, a large safety margin to avoid plating ofmetallic lithium during fast recharge of the high power battery device.This safety margin is additionally of importance for high voltagebatteries based on lithium ion insertion materials according to thepresent invention, since there is a higher probability that a cell in abattery device comprising a large number of cells, which are notindividually monitored by an electronic monitoring circuit and device,may become unbalanced in terms of its ratio of anode-to-cathodecapacity. If a cell were to become unbalanced, the significantlyincreased voltage drop during discharge and the very significantincrease in cell voltage required during charge, before metallic lithiumplating could occur on the cathode or the anode, respectively, providesfor easier detection of an arising problem in a string of cells in abipolar battery according to the present invention compared to standardLi-ion batteries. While increased cell voltage during charge of anunbalanced cell could still lead to premature loss of capacity and/orpower capability, at least it would not affect the safety of thebattery. Safety becomes even more challenging to manage with increasingnumber of cells in series in a bipolar configuration without individualcells or subgroups being monitored. Extensive electronic monitoringwould result in increased cost due to the necessity of attachingmonitoring tabs, wires or the like during the battery assembly processand also due to the cost of the electronic monitoring device and theassociated electrical connections. Therefore, it is desirable tomaximize the number, m, of cells connected in series in avoltage-monitored subgroup in a bipolar configuration, while stillmaintaining good battery life. Due to the specific chemistry andelectrochemistry of the device according to the present invention, theanode-to-cathode capacity ratio, r, is selected with this specificchemistry and electrochemistry in mind. Most prior art rechargeablebattery systems are characterized by an anode-to-cathode capacity ratioof larger than unity, meaning that the battery capacity is limited bythe cathode. This is of particular importance for safety reasons inLi-ion, Ni-MH, Ni—Cd, and lead-acid batteries of the prior art.Anode-limitation of prior art Li-ion batteries could lead to thedeposition of metallic lithium on the anode during charge, which wouldpose a serious safety hazard. We will show however, that embodimentsaccording to the present invention with anode-to-cathode capacity ratiosof smaller than unity can provide unique and advantageous features.Embodiments will be detailed hereunder providing long cycle life andexcellent power, performance over tens of thousands of discharge andcharge pulses while minimizing the cost for electronic monitoring.

The battery according to this invention further comprises a sealstructure providing a leak-proof enclosure and electrical insulationbetween individual cells 20, resulting in a monolithic unit 10. FIG. 1shows as an example how the seal structure 51 encases the bipolar plates22 and end plates 32′, 32″ around their perimeters and provides acomplete enclosure and insulation from cell to cell. In a specificembodiment, the seal structure 51 is created by applying a framestructure 46 around the perimeter of each bipolar plate 22 and each endplate 32′, 32″, followed by stacking the frame structures and theelectrode plates on top of each other and by securing the frames and theelectrode plates to each other around their perimeters by a welding,gluing, moulding or mould injection process or any other process knownto those skilled in the art. In a specific embodiment the seal structure51 consists of a thermoplastic material or of several thermoplasticlayers laminated, welded or otherwise joined together. Suitablematerials include polymers such as polypropylene or any otherpolyolefin, acid-modified polypropylene or polyolefins, polyester,polyvinylidenechloride, SURLYN® (a commercial thermoplastic ionomerresin by DuPont), ACLAR® (a fluoropolymer film by Honeywell) or anyother material with appropriate barrier and electrical insulationproperties, chemical and electrochemical compatibility with the batterycomponents and processing characteristics. The seal structure mayinclude additives or an additional barrier layer to improve the hermeticseal and/or to trap moisture or may be based on resins which arehardened at ambient or above-ambient temperature or by UV light or anyother suitable source of radiation. Additionally, the seal structure mayprovide a section for at least one cell, where gas can accumulate or beabsorbed by suitable getters in case of any parasitic side reactionevolving gaseous compounds.

As stated above, each cell 20 contains a nonaqueous electrolyte solution36. The nonaqueous electrolyte solution 36 is applied before completelysealing all four sides of the monolithic unit 10. The electrolytesolution 36 may comprise a lithium-based salt selected from the groupconsisting of LiPF₆, LiBF₄, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiC(SO₂CF₃)₃,LiClO₄, LiAsF₆, lithium bisoxalatoborate and other lithium borates orany other salt providing a sufficient chemical and electrochemicalstability and sufficient electrolytic conductivity in combination with asuitable organic solvent or a mixture of solvents. The electrolyticconductivity is preferably above 5 mS/cm at 25° C. and most preferablyabove 8 mS/cm at 25° C. The preferred range of concentration of theaforementioned lithium-based salt is between 0.6 and 1.8 M, the mostpreferred range of concentration is between 1.0 and 1.6 M. Preferredsolvents have a boiling point of close to 80° C. or greater, mostpreferably 150° C. or greater, and include propylenecarbonate,ethylenecarbonate, diethylcarbonate, dimethylcarbonate,ethyl-methylcarbonate, gamma-butyrolactone, ethylacetate, ethylbutyrate,ethylpropionate, methylbutyrate, 1,2-dimethoxyethane,1,2-diethoxyethane, 2-methoxyethylether, methoxypropionitrile,valeronitrile, dimethylacetamide, diethylacetamide, sulfolane,dimethysulfite, diethysulfite, trimethylphosphate and ionic liquids.Preferably, the electrolyte solution 36 is inserted into each cell 20under partial vacuum conditions, preferably of −0.2 bar or lower, mostpreferably of −0.8 bar or better. Optionally, the electrolyte solutionand/or at least part or the battery can be cooled down to minimiseevaporation of any solvent.

FIG. 1 exemplifies an embodiment where the monolithic unit containsthree cells in bipolar configuration. In principle, any total number, n,of cells 20 can be connected in series to form a monolithic unit inbipolar configuration as long as means are provided for adequatemonitoring of subgroups. It is the object of the present invention toprovide configurations, where the number, m, of cells in series in avoltage-monitored subgroup is limited to ten or less in order to achievehigh battery life under deep discharge cycling as well as underprolonged pulse charge and discharge conditions. For reasons ofprocessing and limiting the device voltage for operator safety incommercial applications, the total number, n, of cells per monolithicunit may be limited to a maximum of 50, and more preferably of to amaximum of 25.

FIG. 2 shows an example where twenty cells 20 are connected in series toform a monolithic unit 10 in bipolar configuration, where the voltagesof subgroups of m=5 cells in series are monitored. This specificembodiment contains, as an example, five points for voltage monitoring,wherein two of the contact points are provided by any metallic contactto the end plates 32′, 32″ and three of the contacts are provided bymonitoring means 63. Monitoring means 63 can consist of any wire,metallic strip or ribbon electrically connected to the correspondingbipolar plate 22 by any suitable welding, soldering or bonding processor any other process providing a reliable electrical contact. FIG. 2shows an example, where contacting means 63 are partially imbedded inthe seal structure 51. Alternatively, contacting means can be integralpart of the electrode substrate 21′, with the entire substrate or afraction of it extending through the seal structure, as long as adequateelectrical insulation is provided.

Additional power needs may be met by combining monolithic units 10according to the present invention in either series or parallelrelation. In a preferred embodiment, electrical contacts from theelectrochemical storage device to the terminal cables 62′, 62″ isprovided through terminal plates 60′, 60″ and contacting means 81.Terminal plates 60′, 60″ are preferably made of aluminum or any materialproviding good electrical conductivity and electrochemical compatibilitywith the end substrate plates 21 and/or the contacting means 81.Terminal plates 60′, 60″ are preferably much thicker than electrodesubstrate plates 21, 21′, i.e. in the order of 0.1-10 mm, mostpreferably 0.3-1.0 mm. Contacting means 81 include any welding,soldering or bonding process, or mechanical pressure applied directlybetween terminal plates 60′, 60″ and end substrate plate 21 or through acontact element 82. Alternatively, at least one of the terminal plates60′, 60″ and end substrate plates 21 can be roughened, embossed,profiled or otherwise structured to enhance electrical contact. Contactelement 82 can consist of an electrically conductive film, a mat ofelectrically conductive foam, felt, expanded or a woven metal mesh.Materials for contact elements 82 are chosen mainly for their corrosionresistance, their electronic and thermal conductivity and theiravailability and cost. Copper, although suitable for reasons ofelectronic and thermal conductivity, and cost, is not the preferredmaterial because of its long-term electrochemical incompatibility whencontacted to aluminum, particularly in the presence of moisture or othercorrosion-inducing agents. For the present invention, aluminum andnickel are the preferred materials. If-the contacting means comprisesmechanical pressure, such pressure can be provided by a mechanicaldevice including, but not limited to, nuts and bolts, spring loads,shrink tubing, elastic or inelastic straps or a housing containingvacuum of up to minus one atmosphere relative to ambient pressure.Preferred level of compression is in the range of 0.02 MPa to 1 MPa.

Depending on the size of the battery and the application, the batterydevice will additionally comprise fuses, circuit breakers or electronicrelays, temperature sensing devices such as thermistors, optionally inconjunction with an appropriate electronic circuit in order to monitorthe battery device and to assure that voltage, current, and temperatureremain within specified limits. In case of any abnormal behavior of thebattery or parts of the battery, the whole battery or parts of thebattery can be isolated electrically through the circuit breaker orelectronic relay.

The principles of the invention described above, and specificallyclaimed herein, were used to assemble various battery devices consistentwith the above disclosure. The assembly of the devices, as well asseveral alternative structures, will be described below. However, thepresent disclosure is not intended to limit the invention to any of theparticularly disclosed structures, except insofar as the appended claimsare so limited.

In order to construct the EXAMPLES according to principles of thepresent invention, two types of anode end plates with two differentlevels of active material loading (type A1, A2), one type of cathode endplates C and two types of bipolar plates with two different levels ofactive anode material loading (type B1, B2) were prepared. A 50 μm thickfoil of high purity aluminum was primed with a suspension of graphiteand carbon black in an aqueous solution of polysilicate. The suspensionwas coated onto one side of the aluminum foil only for end plates (A1,A2, C) and onto both sides for bipolar plates (B1, B2). After thoroughlydrying the primer layer, the active anode and cathode materials,Li₄Ti₅O₁₂ and Li_(1.05)Cr_(0.10)Mn_(1.90)O₄ respectively, were coated ontop of the primed layer from slurries based on N-methyl-2-pyrrolidinone,PVDF, and carbon to yield coated areas of 100 mm×100 mm. In the case ofend plates, one side only was coated with either anode or cathodematerial. In the case of bipolar plates, one side was coated with anode,and the other with cathode material. All electrode plates were dried andcalendered. TABLE 1, below, gives the nominal capacity for each side ofthe five different types of plates.

TABLE 1 Active material Active material Plate type capacity, anodecapacity, cathode A1 (anode end plate) 210 mAh — A2 (anode end plate)165 mAh — C (cathode end plate) — 190 mAh B1 (bipolar plate) 210 mAh 190mAh B2 (bipolar plate) 165 mAh 190 mAh

Frames of SURLYN® 1652 film (DuPont) were die-cut to outer dimensions of140 mm×140 mm and an inner section of 102 mm×102 mm was cut and removed.An anode plate A1 was then placed between two frames and thermallybonded to the two frames by using a commercially available heated press.In this process, the outermost areas around the perimeters of the twoframes were fused together as well, resulting in an easy-to-handle andeasily stackable framed electrode. This process was repeated with allthe electrode plates (A1,A2,C,B1,B2) required for the examples detailedhereunder. A 110 mm×110 mm piece of microporous polyolefinic separatorwas then positioned on top of each cathode layer and partially over theframe area of the corresponding plate. For each of the electrode plates,the separator was then heat-welded to the frame on two opposite sides.

EXAMPLES 1-8 were prepared according to a common procedure. The onlyvariable parameters were the total number, n, of cells per monolith,connected in series, the anode-to-cathode capacity ratio, r, and thetype of electrolyte solution. In each of the EXAMPLES 1-8, the totalnumber, n, of cells per monolithic unit and the number, m, of cells involtage-monitored subgroup was equal (n=m). All parameters for batteryEXAMPLES 1-8 are summarized in TABLE 2. EC stands for ethylenecarbonate,DEC for diethylcarbonate, DMC for dimethylcarbonate and MPN formethoxypropionitrile. TABLE 3 gives the conductivities and the boilingpoints of the lowest boiling component of the electrolyte systemsemployed for the EXAMPLES described hereunder.

TABLE 2 Electrode Nominal Cell capacity plates n = m voltage R limitedby Electrolyte system EXAMPLE 1 C, B1, A1 5 12.5 V 1.1 Cathode 1 MLiPF₆, 1:1 EC:DEC EXAMPLE 2 C, B1, A1 10   25 V 1.1 Cathode 1 M LiPF₆,1:1 EC:DEC EXAMPLE 3 C, B2, A2 5 12.5 V 0.87 Anode 1 M LiPF₆, 1:1 EC:DECEXAMPLE 4 C, B2, A2 10   25 V 0.87 Anodē 1 M LiPF₆, 1:1 EC:DEC EXAMPLE 5C, B1, A1 5 12.5 V 1.1 Cathode 1 M LiPF₆, 1:1 EC:DMC EXAMPLE 6 C, B2, A25 12.5 V 0.87 Anode 1 M LiPF₆, 1:1 EC:DMC EXAMPLE 7 C, B1, A1 5 12.5 V1.1 Cathode 1 M LiPF₆, MPN EXAMPLE 8 C, B1, A1 5 12.5 V 1.1 Cathode 1.3M LiPF₆, MPN

TABLE 3 Boiling point Conductivity at of lowest boiling Electrolytesystem 24 ± 1° C. component 1 M LiPF₆, 1:1 EC:DEC  7.5 mS/cm 109° C. 1 MLiPF₆, 1:1 EC:DMC 11.7 mS/cm  91° C. 1M LiPF₆, MPN 10.9 mS/cm 166° C.1.3 M LiPF₆, MPN  9.9 mS/cm 166° C.

A framed cathode end plate with its separator attached was laid on aflat surface with the cathode and separator facing upward. (n−1) framedbipolar plates, with their respective separator layer attached, werestacked on top of the cathode end plate, always with their cathode sidesfacing upward and the frame edges being properly aligned. Finally, aframed anode end plate, with its active side facing downward, waspositioned on top of the stack Three sides of the resulting n-cell stackwere then heat-sealed together by applying heat and pressure from thetop and the bottom onto the frame edges. The appropriate amount of anelectrolyte solution specified in TABLE 2 was then injected into each ofthe cells in order to thoroughly wet out the electrodes and theseparator. The assembly was then evacuated close to −1 bar and the openedge sealed under vacuum. This procedure resulted in a n-cell bipolarmonolithic unit of n×2.5 V nominal voltage. Two pieces of 1 mm thick 100mm×100 mm nickel foam mat with 60 ppi pore size were placed onto bothend plates followed by two terminal plates of 1 mm aluminum sheets of100 mm×100 mm size, with a 10 mm wide tab being an integral part of eachsheet. This assembly was placed between two rigid FORMICA® plates andthen into a spring-loaded mechanical compression device, wherecompression corresponding to a 100 kg load was applied. In all EXAMPLES,the compression device was calibrated using a compression load cell fromOMEGADYNE®. All EXAMPLES were tested at an ambient temperature of 22±2°C.

EXAMPLE 1

FIG. 3 shows the capacity output of EXAMPLE 1, a five-cell bipolarbattery under a compression corresponding to a 100 kg load, as afunction of cycle number when the battery device was charged anddischarged at the 1C rate of 190 mA. The initial battery capacity wasclose to the nominal cathode capacity of 190 mAh, confirming thatbatteries according to EXAMPLE 1 are cathode-limited. After 1000complete charge/discharge cycles, the battery capacity was still 85% ofnominal capacity, showing the excellent cycle stability of a five-cellbipolar battery according to the present invention.

A second bipolar battery according to EXAMPLE 1 was tested for its highpower performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 4 showsthe 20C discharge curve of EXAMPLE 1 in comparison with other EXAMPLESof the present invention. The battery run time of EXAMPLE 1 was 46 swhen the cut-off voltage was set to 7.5 V, showing the favorable highpower performance of the EXAMPLE according to the present invention.

A third bipolar battery according to EXAMPLE 1 was tested for its highpower performance over continued high power pulses. After full charge atthe 1C rate, the pulse sequence detailed in TABLE 4 was applied. Resultsare given in TABLE 5 in comparison with other EXAMPLES of the presentinvention. EXAMPLE 1 provided 77,000 15 s pulses at the 20C rate,corresponding to 0.04 A/cm², before the discharge voltage dropped tobelow 7.5 V, showing the favorable stability under continuous high powerstress conditions of the EXAMPLE according to the present invention.

TABLE 4 Pulse step Step description 1 15 s discharge at 20 C rate, stoptest if voltage drops to below n × 1.5 V 2 20 s rest 3 Charge to n × 2.7V 4 10 s rest 5 Increase pulse counter by one unit and continue withstep 1.

TABLE 5 Number of 20 C pulses achieved EXAMPLE 1 77,000 EXAMPLE 2 42,000EXAMPLE 5 >100,000

EXAMPLE 2

FIG. 3 shows the capacity output of EXAMPLE 2, a ten-cell bipolarbattery under a compression corresponding to a 100 kg load, as afunction of cycle number when the battery device was charged anddischarged at the 1C rate of 190 mA. The initial battery capacity wasclose to the nominal cathode capacity of 190 mAh, confirming thatbatteries according to EXAMPLE 2 are cathode-limited. While the cyclestability was very comparable to EXAMPLE 1 over the first few hundredcycles the capacity output of EXAMPLE 2 seriously deteriorated afterabout 400 cycles, showing that ten cells in series, without monitoringthe voltage of smaller subgroups, do not yield adequate batterystability when design parameters of EXAMPLE 2 were employed.

A second bipolar battery according to EXAMPLE 2 was tested for its highpower performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 4 showsthe 20C discharge curve of EXAMPLE 2 in comparison with EXAMPLES 1, 3,and 4. The battery run time of EXAMPLE 2 was 45 s when the cut-offvoltage was set to 15 V, showing that the battery run time isindependent of the number of cells, n, connected in series according tothe present invention.

A third bipolar battery according to EXAMPLE 2 was tested for its highpower performance over continued high power pulses. After full charge atthe 1C rate, the pulse sequence detailed in TABLE 4 was applied. Resultsare given in TABLE 5 in comparison with other EXAMPLES of the presentinvention. EXAMPLE 2 provided 42,000 15 s pulses at the 20C rate,corresponding to 0.04 A/cm², before the discharge voltage dropped tobelow 15 V, showing less favorable stability than EXAMPLE 1 undercontinuous high power stress conditions.

EXAMPLE 3

FIG. 3 shows the capacity output of EXAMPLE 3, a five-cell bipolarbattery under a compression corresponding to a 100 kg load, as afunction of cycle number when the battery device was charged anddischarged at the 1C rate of 190 mA. Note that the nominal C-rate ofEXAMPLE 3 was based on cathode capacity, in the same way as for EXAMPLES1 and 2. The initial capacity of EXAMPLE 3 was significantly lower thanfor EXAMPLES 1 and 2. It was close to the nominal anode capacity of 165mAh, confirming that batteries according to EXAMPLE 3 are anode-limited.After 1000 complete charge/discharge cycles, the battery capacity wasstill 78% of the initial one, showing the excellent cycle stability of afive-cell bipolar battery according to the present invention.

A second bipolar battery according to EXAMPLE 3 was tested for its highpower performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 4 showsthe 20C discharge curve of EXAMPLE 3 in comparison with EXAMPLES 1, 2,4. The battery run time of EXAMPLE 3 was 54 s when the cut-off voltagewas set to 7.5 V, showing the favorable high power performance of theEXAMPLE according to the present invention. In comparison with EXAMPLE 1(r=1.1), the battery run time of EXAMPLE 3 (r=0.87) was longer and thedischarge curve flatter, showing that an anode-to-cathode capacity ratioof r<1 can be beneficial for certain applications, particularly atelevated power.

EXAMPLE 4

FIG. 3 shows the capacity output of EXAMPLE 4, a ten-cell bipolarbattery under a compression corresponding to a 100 kg load, as afunction of cycle number when the battery device was charged anddischarged at the 1C rate of 190 mA Note that the nominal C-rate ofEXAMPLE 4 was based on cathode capacity in the same way as for EXAMPLES1 and 2. The initial capacity of EXAMPLE 4 was significantly lower thanfor EXAMPLES 1 and 2. It was close to the nominal anode capacity of 165mAh, confirming that batteries according to EXAMPLE 4 are anode-limited.While the cycle stability was comparable to EXAMPLE 3 over the first400-500 cycles, the capacity output of EXAMPLE 4 seriously deterioratedafter about 680 cycles. In comparison with EXAMPLE 2 (r=1.1), the cyclelife of EXAMPLE 4 (r=0.87) was improved by about 200 cycles, showingthat r<1 can be beneficial for achieving higher battery cycle life.

A second bipolar battery according to EXAMPLE 4 was tested for its highpower performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 4 showsthe 20C discharge curve of EXAMPLE 4 in comparison with EXAMPLES 1-3.The battery run time of EXAMPLE 4 was 54 s when the cut-off voltage wasset to 25 V, showing the favorable high power performance of the EXAMPLEaccording to the present invention. In comparison with EXAMPLE 2(r=1.1), the battery run time of EXAMPLE 4 (r=0.87) was longer and thedischarge curve flatter, showing again that an anode-to-cathode capacityratio of r<1 can be beneficial for certain applications, particularly atelevated power.

EXAMPLE 5

A bipolar battery according to EXAMPLE 5 was assembled using anelectrolyte solution with a higher electrolytic conductivity than in thecase of EXAMPLES 1-4. EXAMPLE 5 was tested for its high powerperformance. It was fully charged at the 1C rate and then discharged atthe 20C rate, corresponding to 0.04 A/cm². FIG. 5 shows the 20Cdischarge curve of EXAMPLE 5, in comparison with EXAMPLE 1, where thelatter was based on a lower conductivity electrolyte solution. Thebattery run time of EXAMPLE 5 was 64 s when the cut-off voltage was setto 7.5 V, showing the very favorable high power performance of theEXAMPLE according to the present invention.

A second bipolar battery according to EXAMPLE 5 was tested for its highpower performance over continued high power pulses. After fill charge atthe 1C rate, the pulse sequence detailed in TABLE 4 was applied. Resultsare given in TABLE 5 in comparison with other EXAMPLES of the presentinvention. EXAMPLE 5 provided 100,0000 15 s pulses at the 20C rate,corresponding to 0.04 A/cm², without the voltage dropping to below 7.5V, showing the excellent stability under continuous high power stressconditions of the EXAMPLE according to the present invention.

EXAMPLE 6

Another bipolar battery was assembled using the same electrolytesolution and the same number of cells in series (n=5) as for EXAMPLE 5.In contrast to EXAMPLE 5 (r=1.1), EXAMPLE 6 (r=0.87) was howeveranode-limited. EXAMPLE 6 was tested for its high power performance. Itwas fully charged at the 1C rate and then discharged at the 20C rate,corresponding to 0.04 A/cm². FIG. 5 shows the 20C discharge curve ofEXAMPLE 6 in comparison with EXAMPLES 1 and 5. The battery run time ofEXAMPLE 6 was 75 s when the cut-off voltage was set to 7.5 V, showingthe excellent high power performance of the EXAMPLE according to thepresent invention. In comparison with EXAMPLE 5, the battery run time ofEXAMPLE 6 was longer and the discharge curve flatter, showing that ananode-to-cathode capacity ratio of r<1 can be beneficial for certainapplications, particularly at elevated power rates.

EXAMPLE 7

Another bipolar battery was assembled using an electrolyte solution witha higher electrolytic conductivity than in the case of EXAMPLES 1-4. Incontrast to EXAMPLES 5 and 6, the solvent system of EXAMPLE 7 had a muchhigher boiling point (see TABLE 3). EXAMPLE 7 was tested for its highpower performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 6 showsthe 20C discharge curve of EXAMPLE 7, in comparison with EXAMPLE 5. Thebattery run time of EXAMPLE 7 was 75 s when the cut-off voltage was setto 7.5 V, showing the excellent high power performance of the EXAMPLEaccording to the present invention. In comparison with EXAMPLE 5, theaverage discharge voltage of EXAMPLE 7 was significantly higher, despitethe much higher boiling of the solvent system and the slightly lowerelectrolyte conductivity, because the electrolyte system of EXAMPLE 7offers overall more favorable Li⁺ transport properties.

EXAMPLE 8

Another bipolar battery was assembled using the same solvent system asfor EXAMPLE 7. In comparison to EXAMPLE 7, however, the electrolyteconcentration of EXAMPLE 8 was higher resulting in a slightly lowerelectrolyte conductivity (see TABLE 3). EXAMPLE 8 was tested for itshigh power performance. It was fully charged at the 1C rate and thendischarged at the 20C rate, corresponding to 0.04 A/cm². FIG. 6 showsthe 20C discharge curve of EXAMPLE 8, in comparison with EXAMPLES 5 and7. The battery run time of EXAMPLE 8 was 92 s when the cut-off voltagewas set to 7.5 V, showing the outstanding high power performance of theEXAMPLE according to the present invention. In comparison with EXAMPLE5, the average discharge voltage of EXAMPLE 8 was significantly higherdespite the much higher boiling of the solvent system and the lowerelectrolyte conductivity because the electrolyte system of EXAMPLE 8offers overall more favorable Li⁺ transport properties. In addition, thehigher electrolyte concentration of EXAMPLE 8 in comparison to EXAMPLE7, provides a mechanism to limit concentration polarization during highpower discharge events, thus resulting in overall better cell capacityutilization.

EXAMPLE 9

In order to demonstrate that the present invention is suitable forlarge-footprint batteries, another example was assembled based on muchlarger electrodes than used for EXAMPLES 1-8. A 50 μm thick foil of highpurity aluminum was primed with a suspension of graphite and carbonblack in an aqueous solution of polysilicate. The suspension was coatedto one side of the aluminum foil only for end plates and to both sidesfor bipolar plates to yield a primed area of 294 mm×169 mm. Theelectrodes were based on Li₄Ti₅O₁₂ and Li_(1.05)Cr_(0.10)Mn_(1.90)O₄,coated on top of the primed layer from slurries based onN-methyl-2-pyrrolidinone, PVDF and carbon to one side for end plates orto two sides for bipolar plates to yield for each side coated areas of294 mm×169 mm. Cathode nominal capacity was 0.94 Ah and anode nominalcapacity was 1.04 Ah, resulting in an anode-to-cathode capacity ratio of1.1. All electrode plates were dried and calendered.

Frames of SURLYN® 1652 film (DuPont) were die-cut to outer dimensions of377 mm×214 mm and an inner section of 303 mm×178 mm was cut and removed.The distance between three of the frame edges and the inner section was18-19 mm, while it was 55 mm between the fourth edge of the frame andthe inner section. An anode end plate was then placed between two framesby centering the coated area with respect to the open frame area. Theanode end plate was then thermally bonded to the two frames by using acommercially available heated press. In this process the areas aroundthe perimeters of the two frames, extending over the substrate plates,were fused together as well, resulting in an easy-to-handle and easilystackable framed electrode. This same process was repeated with fourbipolar plates and a cathode end plate. A 183 mm×308 mm piece ofmicroporous polyolefinic separator was then positioned on top of eachcathode layer and partially over the frame area of the correspondingplate. For each of the electrode plates, the separator was thenheat-welded to the uncoated substrate on two opposite sides. A framedcathode end plate with its separator attached was laid on a flat surfacewith the cathode and separator facing upward. Four framed bipolarplates, with their respective separator layer attached, were stacked ontop of the cathode end plate, always with their cathode sides facingupward and the frame edges being properly aligned Finally, a framedanode end plate, with its active side facing downward, was positioned ontop of the stack. Three sides of the resulting five-cell stack were thenheat-sealed together by applying heat and pressure from the top and thebottom onto the frame edges over a width of about 10 mm. The appropriateamount of 1 M LiPF₆ dissolved in 1:1 EC:DMC was then injected into eachof the cells in order to thoroughly wet out the electrodes and theseparator. The assembly was then cooled down to around −18° C. andevacuated close to −1 bar and the open edge sealed under vacuum,resulting in a fourth sealed edge area of about 10 mm width; Thisprocedure resulted in a 5-cell bipolar monolithic unit of 12.5 V nominalvoltage and 0.94 Ah nominal capacity with a 35-37 mm wide section alongthe forth side as head space. This head space could accommodate anygaseous products possibly formed due to operation at very hightemperatures or under abuse conditions. The monolithic unit was furthersealed around its entire perimeter with a laminate ofpolypropylene/aluminum/polyester, which itself was attached in ahermetic way to the outside of the cathode and the anode end plate. Twopieces of 1 mm thick 295 mm×170 mm nickel foam mat with 60 ppi pore sizewere placed onto both end plates followed by two terminal plates of 1 mmaluminum sheets of 295 mm×170 mm size, with a 20 mm wide tab being anintegral part of each sheet. This assembly was placed between two rigidFORMICA® plates and then into a spring-loaded mechanical compressiondevice, where compression corresponding to a 1500 kg load was applied.The compression device was calibrated using a compression load cell fromOMEGADYNE®.

FIG. 7 shows the capacity output of EXAMPLE 9, a five-cell bipolarbattery under a compression corresponding to a 1500 kg load, as afunction of cycle number when the battery device was charged anddischarged at 1 A at an ambient temperature of 22±2° C. The initialbattery capacity was close to the nominal cathode capacity of 0.94 Ah,confirming that batteries according to EXAMPLE 9 are cathode-limited.After 3000 complete charge/discharge cycles the battery capacity wasstill 0.88 Ah, corresponding to more than 90% of its nominal capacity,showing the outstanding cycle stability of a large footprint five-cellbipolar battery according to the present invention.

The foregoing description, drawings and examples merely explain andillustrate the invention and the invention is not limited thereto exceptinsofar as the appended claims are so limited, as those skilled in theart who have the present disclosure before them will be able to makemodifications and variations therein without departing from the scope ofthe invention.

1. A bipolar high power battery, comprising: a) at least one group of nstackable electrochemical energy storage cells, connected in series, thecells having: a lithium ion insertion cathode on a current collectorsubstrate and a lithium ion insertion anode on a current collectorsubstrate, with an anode-to-cathode capacity ratio r; a separatormaterial associated between the anode and the cathode; and anelectrolyte system; wherein 2≦n≦50 and 0.6≦r<1; b) a leak-proof sealstructure; c) means for voltage monitoring of subgroups of m storagecells connected in series where 2≦m≦10 and m≦n; and d) means for keepingthe battery under compression.
 2. The device according to claim 1,wherein the anode includes a lithiated titanium oxide.
 3. The deviceaccording to claim 2, wherein the lithiated titanium oxide is of thespinel type.
 4. The device according to claim 3, wherein the cathodeincludes a lithium manganese oxide.
 5. The device according to claim 4,wherein the lithium manganese oxide is of the spinel type.
 6. The deviceaccording to claim 5, wherein the cathode comprises a lithium insertionmaterial having a dopant selected from the group consisting of B, Al,Mg, Ca, Zn, Fe, Mn, Ni, Co, and Cr.
 7. The device according to claim 1,wherein both the anode and the cathode have a porosity between 30% and60% each.
 8. The device according to claim 1, wherein the deviceadditionally comprises at least one conductive primer layer, wherein theconductive primer layer is positioned between at least one of the anodeand the adjacent current collector and the cathode and the adjacentcurrent collector.
 9. The device according to claim 8 having a chargeand discharge capability of at least 0.04 A/cm² for more than 60s. 10.The device according to claim 9, wherein the compression means comprisesa mechanical compression device.
 11. The device according to claim 10,wherein the level of compression is between 0.02 MPa and 1 MPa.
 12. Thedevice according to claim 11, wherein the electrolyte system comprises anonaqueous electrolyte system.
 13. The device according to claim 12,wherein the electrolyte system comprises a lithium-based salt selectedfrom the group consisting of LiPF₆, LiBF₄, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂,LiC(SO₂CF₃)₃, LiClO₄, LiAsF₆, lithium bisoxalatoborate and other lithiumborates.
 14. The device according to claim 13, wherein the concentrationof the lithium-based salt is between 1.0 and 1.6 M.
 15. The deviceaccording to claim 14, additionally comprising at least one electrolytesolvent, wherein the at least one solvent associated with theelectrolyte is selected from the group consisting of propylenecarbonate,ethylenecarbonate, diethylcarbonate, dimethylcarbonate,ethyl-methylcarbonate, gamma-butyrolactone, ethylacetate, ethylbutyrate,ethyipropionate, methylbutyrate, 1,2-dimethoxyethane,1,2-diethoxyethane, 2-methoxyethylether, methoxypropionitrile,valeronitrile, dimethylacetamide, diethylacetamide, sulfolane,dimethysulfite, diethysulfite, trimethylphosphate and ionic liquids. 16.The device according to claim 15, wherein the electrolyte system has aconductivity of at least 8 mS/cm at 25° C.
 17. The device according toclaim 16, wherein the seal structure comprises at least one polymerselected from the group consisting of thermoplastic polymers,thermoplastic ionomers, duroplastic polymers, and resins.
 18. The deviceaccording to claim 17, wherein the seal structure comprises at least onelayer of barrier material, associated with the device in a hermetic way.19. The device according to claim 18, wherein the barrier materialconsists of a composite comprising at least one heat-sealable layer, onebarrier layer, and one additional insulating layer.
 20. The deviceaccording to claim 1, wherein the seal structure may provide a sectionfor each cell where gas can accumulate or be absorbed by getters. 21.The device according to claim 1, comprising: a) at least two groups ofn_(l) to n_(z) stackable electrochemical energy storage cells, connectedin series within each group, the cells having: a lithium ion insertioncathode on a current collector substrate and a lithium ion insertionanode on a current collector substrate, with an anode-to-cathodecapacity ratio r; a separator material associated between the anode andthe cathode; and an electrolyte system; where z is any integer,2≦n_(i)≦50, 1≦i≦z, and 0.6≦r<1; b) a leak-proof seal structure; c) meansfor voltage monitoring of subgroups of m cells connected in series where2≦m≦10 and m≦n_(i); and d) means of keeping the battery undercompression.
 22. The device according to claim 21, wherein the at leasttwo groups of n_(l) to n_(z) stackable electrochemical energy storagecells are configured in any combination of series and parallelconnections.
 23. The device according to claim 22, wherein all n_(l) ton_(z) numbers are identical.
 24. The device according to claim 21,wherein the at least two groups of n_(l) to n_(z) stackableelectrochemical energy storage cells are electrically connected bycontacting means.
 25. The device according to claim 24, whereincontacting means comprise a conductive sheet of material held in placeand providing electrical contact to and in-between device end plates bythe means for keeping the battery under compression.